argoproj/argo-workflows · error

failed to unmarshall JSON expression: %w

Error message

failed to unmarshall JSON expression: %w

What it means

expressionReplaceCore could not JSON-unmarshal the raw expression text (it is embedded in a JSON-marshaled template and must first be unescaped); the expression contains escapes that do not form a valid JSON string. If allowUnresolved were true the tag would pass through instead.

Source

Thrown at util/template/expression_template.go:228

		if rv.Kind() == reflect.String {
			if IsPlaceholder(rv.String()) {
				shouldAllowFailure = true
				return false
			}
		}
		return true
	})

	log := logging.RequireLoggerFromContext(ctx)
	// The template is JSON-marshaled. This JSON-unmarshals the expression to undo any character escapes.
	var unmarshalledExpression string
	err := json.Unmarshal(fmt.Appendf(nil, `"%s"`, expression), &unmarshalledExpression)
	if err != nil && allowUnresolved {
		log.WithError(err).Debug(ctx, "unresolved is allowed")
		return fmt.Fprintf(w, "{{%s%s}}", kindExpression, expression)
	}
	if err != nil {
		return 0, fmt.Errorf("failed to unmarshall JSON expression: %w", err)
	}

	varNameNotInEnv := anyVarNotInEnv(unmarshalledExpression, env)
	if varNameNotInEnv != nil && allowUnresolved {
		// this is to make sure expressions don't get resolved to nil or an empty string when certain variables
		// don't exist in the env during the "global" replacement.
		// See https://github.com/argoproj/argo-workflows/issues/5388, https://github.com/argoproj/argo-workflows/issues/15008,
		// https://github.com/argoproj/argo-workflows/issues/10393, https://github.com/expr-lang/expr/issues/330
		log.WithField("variable", *varNameNotInEnv).Debug(ctx, "variable not in env but unresolved is allowed")
		return fmt.Fprintf(w, "{{%s%s}}", kindExpression, expression)
	}

	program, err := expr.Compile(unmarshalledExpression, expr.Env(env))
	// This allowUnresolved check is not great
	// it allows for errors that are obviously
	// not failed reference checks to also pass
	if err != nil && !allowUnresolved && !shouldAllowFailure {
		return 0, fmt.Errorf("failed to evaluate expression: %w", err)

View on GitHub (pinned to 35bff19146)

Solutions

1. Fix escaping in the expression tag so it is a valid JSON string after marshalling
2. Avoid raw control characters or unbalanced escapes inside {{= ...}}

When it happens

Trigger: Thrown at util/template/expression_template.go:228 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of argoproj/argo-workflows@35bff19146 (2026-09-03). Data as JSON: /api/errors/6e6ffb6813bfa50a. Report an issue: GitHub.